We assume an initial electrons spectrum with a power law shape, \(N_e(p,t_0)=k_0 p^{-s}\)  with \(s=2.7\) , and initial values of the magnetic field and the thermal density so that at the present time they are equal respectively to the equipartion value \(B=4.7\)  \(\mu \) G [1]} and to a reference value chosen in the range \(10^{-6}-10^{-3}\)  cm\(^{-3}\) . We therefore calculate the electrons spectrum after a time of the order of the age of the bubble, estimated to be \(\sim 160\)  Myr from X-ray observations [2]} and MHD simulations [3]}, and choose the electrons normalization \(k_0\)  and the Fermi-II acceleration parameter \(\chi \)  in order to match the observed spectrum of the radio emission, with the best parameters values resulting to be \(k_0=1.5\times 10^{-3}\)  cm\(^{-3}\)  and \(\chi =3.5\times 10^{-16}\)  s\(^{-1}\)  [4]}.
